<!DOCTYPE html>
<style>
.outer {
    width: 600px;
    height: 100px;
    background-color: green;

    display: flex;
}

.inner {
    max-width: -webkit-fill-available;
    margin-right: 1000px;

    width: 700px;
    height: 100px;

    background-color: red;
}
</style>
<body>
<p>You should see no red.</p>
<div class="outer">
    <div class="inner">
    </div>
</div>
